Magnetic resonance imaging (MRI) is a known modality for acquiring images of the inside of the body of a living patient. The basic components of an MRI device are a basic field magnet, a gradient system and a control system that produces pulses and controls the currents in the gradient coils that produce the pulse sequences. The time-variable coil currents achieve amplitude values of up to several 100 A and are subject to frequent and rapid changes in the direction of the current with rise and decay rates of several 100 kA/s. Given the presence of a basic magnetic field, these currents in the gradient coils cause vibrations due to Lorentz forces, which cause an acoustic-noise, by vibrating components of the apparatus.
Exposure to such an acoustic-noise can be extremely stressful for a patient and especially to newborn or premature babies. Exposure to a sudden, unexpected noise can cause startle reaction with stress responses and can cause non intentional injuries. A build up of stress can in turn reduce the level of oxygen reaching the baby's brain. Stress and decreased oxygen levels have associated health risks including increased rate of calorie burn and, in extreme cases, death.
Developments in the field of MRI are meant for shortening the measuring time and improving the image quality which involve a boost of the currents in the gradient coils, causing the acoustic-noise level to increase.
Previous investigations attempted to reduce the acoustic-noise by modifying the transmission path, i.e., modifying the mechanical structure of the MRI apparatus. These modifications were roughly implemented on the basis of empirical values. Prior art attempts to reduce the acoustic-noise level include, e.g., Plattel, WO 200907918, which discloses a method of performing an MRI scan with acoustic noise reduction in a magnetic resonance imaging system, the noise resulting from an operation of gradient coils of the magnetic resonance imaging system. Plattel's method comprising: measuring an acoustic noise, the acoustic noise resulting from an operation of the gradient coils; determining an acoustic response function, the acoustic frequency response function relating the measured noise to an excitation characteristic used for the operation of the gradient coils; calculating a set of Sound Pressure Levels (dB) using the acoustic response function, each sound pressure level of the set of sound pressure levels resulting as output of the response function from a different excitation characteristics as input to the response function; determining a sound pressure level minimum in the set of calculated sound pressure levels; and performing the magnetic resonance imaging scan using the excitation characteristics associated with the determined sound pressure level minimum.
Dietz, U.S. Pat. No. 6,407,548, discloses a method for operating a magnetic resonance tomography apparatus that contains a basic field magnet, a gradient system with gradient coils and a control system that controls the currents in the gradient coils, among other things, on the basis of pulse sequences, noise that is caused by a pulse sequence upon implementation thereof is identified before a start of the pulse sequence. When an identified noise lies above a selectable value, the pulse sequence is modified, so that the modified pulse sequence does not exceed the selectable value when it is implemented.
The above mentioned inventions disclose methods for reducing the acoustic noise by modifying the scanning pulse-sequences thereby interfering with the optimal scan requirements. There is thus a long felt need for an operating method for the MRI scan that can ease the patient's exposure to such acoustic-noise level, while optimizing the scan quality.